Thermostatic control switch having wiping contact action



A ril 6, 1965 c. s. MERTLER THERMOSTATIG CONTROL SWITCH HAVING WIPING CONTACT ACTION Filed Sept. 20, 1961 Fig.

3 INVENTOR.

CHARLES s. MERTLER BY W, 12ml:

Fig 3 BTT United States Patent 3,177,316 THERMUSTATIC CUNTROL SWITCH HAVING 11 '3" CONTACT ACTEUN (l'harles S. Mertier, Mansfield, Ohio, assignor to Stevens Manufacturing Qornpany, Inc. Filed Sept. 28, 1961, Ser. No. 139,547 Claims. (Cl. 299-113) This invention relates in general to thermostatic control switches and, more particularly, to a thermostatic switch having special provisions for inhibiting the sticking of contacts.

Thermostatic control switches are used in many applications including use of a bimetallic member actuating a contact. The contact may be carried on one end of the member which deflects upon temperature changes in a direction generally transverse to the length direction of the member. This, in the usual case, is a direct separation of the contacts. In many cases, an arc is drawn between the contacts as they are closed or separated, espe cially for inductive loads. Some variable in the operating condition may cause the contacts to momen tarily close after they have first started to open and the arc has been drawn. Also, the contacts may bounce as they are closing. Such closing or temporary re-closing may tend to partially weld together the contacts because of the heat of the arc. Accordingly, the prior art has known many thermostatic switches which have trouble in sticking of the contacts caused by this form of welding together under adverse operating conditions.

Accordingly, an object of the invention is to inhibit the sticking of contacts as moved by a thermostatic switch.

Another object of the invention is to provide movement in two directions generally at the instant of opening of thermostatic switch contacts to aid in the opening of such contacts.

Still another object of the invention is to provide a longitudinal as well as a lateral motion to a contact movable by a bimetallic member.

Another object of the invention is to provide a transverse arm portion on a bimetallic member with heat predominantly established at the transverse arm member so that a longitudinal movement as well as a transverse movement is eflect'ed by a contact carried on the bimetallic member.

Another object of the invention is to provide a thermostatic switch construction employing contacts with means to provide a wiping action to the contacts.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a plan view of a thermostatic switch embodying the invention and incorporating a schematic circuit diagram;

FIGURE 2 is an isometric view of the bimetallic structure of the thermostatic switch;

FIGURE 3 is a sectional view on line 3-3 of FIG- URE 1; and,

FIGURE 4 is an enlarged partial plan view of the bimetallic structure.

FIGURES 1, 2, 3 and 4 show a thermostat switch it? incorporating the invention and including an insulated housing 1 1 having a base 12 and raised peripheral walls 13. A cover, not shown, may be fastened at holes 14 to enclose the switch parts. A bimetallic U-shaped structure 16 is incorporated in'the switch lit and is best shown in FIGURE 2. This bimetal structure includes first and second legs 17 and 18 joined together by an insulating bar 19 and rivets 2% to form the U-shaped ice structure. The first leg l7 has a first end 21 carrying a first movable contact 22. The second end 23 of the first leg 17 is that which is riveted to the insulating bar 19. A narrowed portion 26 is closely adjacent the first end 21 of the first leg 17. The second leg 18 has first and second ends 24 and 25 with the second end 25 being that which is connected to the insulating bar 1d. A resilient support blade 28 which conveniently may be made of metal has first and second ends 29 and 30. The first end 29 of the support blade 25 is fixedly attached, such as by welding, to the first end 24 of the bimetallic leg 18 so that this support blade 28 supports the entire bimetallic U-shaped structure 16. A mounting flange 31 is a part of the second end 30 and is fastened in any suitable manner such as by rivets 32 to the base 12. As seen in FIGURE 1, the bimetallic U-shaped structure 16 is disposed generally in a plane perpendicular to the base 12. A flexible pigtail conductor 33 has one end connected to the second end 23 of the bimetallic leg 17 at the rivet 20.

A first fixed contact as is mounted on a screw 37 with the screw passing through a first terminal 38 fixedly carried in the base 12. This first terminal passes completely through the base 12 for external connection to this first terminal 38. The screw 37 is for adjustment purposes of the first fixed contact 36 for calibration of the thermostat and a lock nut 39 maintains this calibration. A permanent magnet at is mounted just to the rear of the first fixed contact 36 and cooperates with a magnetic armature 41 just to the rear of the first movable contact 22. The other end of the flexible pigtail 33 is fastened to a second terminal 42 fixedly carried in the base 12 and extending therethrough for external electrical connection.

Third, fourth, fifth, sixth and seventh terminals 43, 44, 45, 46 and 47, respectively, are fixedly mounted in the base 12 and extend therethrou-gh for external electrical connection. A switch blade 50 has one end fixed to the third terminal 43 and the other end is movable and carries a second movable contact 51. The second movable contact 51 cooperates with .a second fixed contact 52 mounted on the fourth terminal 44. An auxiliary blade 53 moves with the switch blade 59 and the movable end 54 thereof makes contact with the fifth terminal 45. A pilot circuit switch blade 55 is mounted on the seventh terminal 47 and a movable end 58 thereof makes contact with a contact 59 on the sixth terminal 4-6. This pilot circuit switch blade 55 carries an insulator button 60 for movement in accordance with movement of the switch blade 50.

A rotary shaft 63 is journa-lled in the base 12 and carries a first and a second rotary cam 64 and 65, respectively. The first rotary cam 64 engages a bent medial portion as on the support blade 28 which acts as a cam follower. The cam 64 has a notch 67 and in FIGURE 1 this notch is shown positioned to be in cooperation with the cam follower 66 so as to establish the first contacts 22 and 36 widely separated and in an off condition. The first cam 64 has a variable radius relative to the shaft 63 to variably adjust the position of the first movable contact 22 relative to the first fixed contact 35.

The second cam acts on a bent medial portion 69 of the switch blade 50 as a cam follower to move this switch blade 5th. The second cam 65 has a notch 70 and FIG- URE 1 shows this notch in cooperation with the cam follower 69 so that the second contacts 5:. and 52 are established widely separated for an off condition of the thermostat it Smaller notches 71 are also established at different points on the periphery of the second cam 65 to give a detent or sensory indication to the operator to a of indicate the boundary between different heat ranges. The main cam surface of the cam 65, when in cooperation with the cam follower 69, establishes the second cont-acts 51 and 52 in the closed position and also establishes closed the auxiliary blade 53 with the fifth terminal 45 and the pilot circuit switch blade 55 with the sixth terminal as.

The FIGURE 1 is a combined schematic and circuit diagram of the switch and shows that the first and fourth terminals 38 and i are connected to opposite ends of an electrical resistance unit '72 which may be surface heating unit of an electric range. A voltage supply source 73 may be an A.C. or DC. source but is shown as an AC. source having a neutral terminal 74 and first and second line terminal 75 and 76. The first line terminal 75 is connected to the second terminal 42 and the second line terminal 7c is connected to the third terminal 43. When the contacts are closed, this will provide energization to the surface heating unit 72 from the first and second line terminals 75 and 76. For example, this may be 230 volt energization. The auxiliary switch blade 53 may be used to control a circuit to a pilot light '77 from the input neutral terminal 74, which, for example, may provide 115 volt energization. The pilot circuitswitch blade 55 is a separate insulated circuit which may housed to control a circuit connected to conductors 7% for any control or indicating purposes. The narrowed portion 26 is a'portion of reduced cross sectional area disposed closer to the first end 21 of the leg 17 than to the second end 23 thereof. This reduced cross sectional area portion includes a U-shaped arm 81 which includes first and second transverse portions $2 and 83 joined by a U-shaped bend S4.

The bimetal leg 17 may be considered as a control bimetal leg to control the actuation of the contact 22. The U-shaped arm 81 is bent so that it is generally perpendicular to the bimetal leg 17 and directed toward the fixed contact 36 rather than away from it. The U-shaped arm fill includes the U-shaped bend 84 which is bent flat wise approximately 180 and, hence, this may be considered a loop of at least 180. This loop tends to close or become smaller upon being heated. With the narrowed portion 26 co-extensive with the U-shaped arm 81, this provides a portion of the lateral arm which is of reduced cross sectional area.

OPERATION When the shaft 63 is rotated counterclockwise from the position shown in FIGURE 1, the cam 64 cooperating with the support blade 28 at the cam follower as will cause the contacts 22 and 36 to close. Also, the cam s5 closes the second contacts 51 and 52. As seen in FIGURE 1, this establishes a closed circuit with voltage being applied to the surface heating unit 72. Current flows through the bimetallic leg 17 and the flexible conductor 33 and this flow of current starts to heat the bimetallic leg 17. The initial heating of this leg 17 is at the narrowed portion 26 and because this is positioned close to the movable contact 22, the transverse deflectional urging caused by such heating is minimized. The bimetallic leg 17 is so positioned that heating thereof causes movement of the contact 22 away from contact as and, hence, this heating will eventually open the circuit.-

The heating of the U-shaped arm 81 tends to close the loop of this U-shaped arm and, hence, the deflection is to the left as viewed in FIGURE 4, as indicated by arrow 85. Since this U-shaped arm, and at least the transverse portion 83 is of reduced cross sectional area, the initial heating is primarily in this portion. Thus,

7 the initial deflection is primarily in accordance with the arrow $5. This provides longitudinal movement to the contact 22. The ultimate heating of the bimetal leg 17 provides the usual transverse movement to the contact 22 in accordance with the arrow 86 and this is the usual movement establishing opening of the contacts 22 and 36.

this raises the current approximately 5% and this increased The U-shaped arm 81 and the fact that the initial heating is primarily at this point is that which establishes both a longitudinal and a transverse movement to the movable contact 22 to, thus, aid in opening the contacts despite any tendency to weld together.

The U-shaped arm 81 and the reduced cross sectional area portion 26 are shown as being at the same location and, hence, co-extensive. The U-shaped arm 81 thus gives a wiping action to the contacts to aid in keeping them clean for long life.

The narrowed portion 26 is located close to the movable contact 22 and this is primarily responsible for only one or two cycles of operation before the operating temperature of the heating element or load 72 is reached. In one thermostatic switch constructed according to the invention, the operating temperature was reached in one minute for a particular wattage heating unit 72. Without this narrowed portion 26, a typical operation would be that 12-15 cycles of operation are required before the operating temperature of the heating unit 72 is reached. This takes a considerably longer period of time. Thus, the narrowed portion 26 provides quick Warm-up of the heating unit 72 yet, without overshoot, because the initial deflection of the entire bimetal leg 17 is delayed upon initial passage of current therethrough.

Both bimetal legs 17 and 18 deflect in the same direction upon, temperature changes and, therefore, the bimetal leg 13 may be considered to be an ambient temperature may undergo considerable change during cooking operations.

The bimetallic leg 17 is temperature responsive to load current flow and responsive to the current flow through this leg to cycle the contact 22. This leg also acts as a proportioning bimetal to maintain a substantially constant wattage on the heating unit 72. If, for example, the input voltage at terminals 75 and 76 increases 5%, then current through the bimetallic leg 17 causes it to heat faster and in so doing, the contacts 22 and 36 are closed a shorter proportion of the time. During this closed condition of the contacts 22 and as, of course, the current is flowing and causing heating both of the heating unit 72 and the bimetallic leg 17. Upon sufiicient heating of the bimetallic leg 17, it moves to open the contacts 22 and 36 and therefore both the leg 17 and the heating unit 72 cool. The magnet an and armature 41 provide a relatively quick make and break to the contacts 22 and 36 because as the contact 22 nears the contact 36 during cooling of the leg 17, the magnetic attraction of the magnet 40 for the armature 41 will reach a point at which it is sufficient to quickly pull the contacts closed. Conversely, as the bimetallic leg 17 heats up by passage of current, it increases its urge to move the contact 22 away from contact 36. A point will bereached whereat this internal stress of the leg'17 eventually overcomes the magnetic attraction and thus the contacts 22 and as are quickly broken. This minimizes arcing at the contacts 22 and 3b and, hence, minimizes pitting and burning.

It will be noted that the entire bimetallic U-shaped structure 16 is capable of being bodily moved relative to the housing 11 since neither end of either leg 17 or 18 T able contact 22 moves primarily in response to current flow through the bimetallic leg 17 and the first end as of the bimetallic leg 18 moves in response to changes in position of the support blade 28.

A calibrated knob, not shown, may be attached to the shaft 63 for adjustment purposes and it will be seen that the entire switch may be continuously controlled without any steps throughout the complete range of operation.

The rotatable cam 64 has a variable radius from the shaft 63 and is proportioned such that upon initial counterclockwise rotation of the shaft 63, the contacts 22 and 3d are closed when the unit is cold. The contacts 22 and 36, however, are only lightly pressed together in this condition and, therefore, only a fairly low average temperature of the bimetallic leg 17 is necessary to cause the contacts 22 and 36 to cycle on and off. If the shaft 63 is rotated nearly 360, however, the contacts 22 and 3d are pressed quite tightly together and, therefore, considerable heat is required in the bimetallic leg 17 to open the contacts 22 and 36. This means that a much higher operating temperature is achieved.

It will be noted that many different forces act on the first movable contact 22, namely, the rotatable cam 64 for setting the desired operating point, the ambient temperature compensating means as established by the second leg 13, the cycling means as determined by current flow through the temperature responsive leg 17 which also includes the proportioning means to maintain substantially constant wattage on the heating unit 72 and which includes the narrowed portion 26 to delay initial cycling of the contact 22, the U-shaped arm 81 to provide longitudinal movement to contact 22, and the magnet 40 to establish quick make and break of the contacts 22 and 36.

The adjustingscrew 37 may be adjusted from outside the housing 11 and may conveniently be adjusted at the factory during manufacture and then may be locked in place by the lock nut 3%.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by Way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said control bimetal leg, a second contact carried by said base for cooperation with said movable contact, a lateral arm portion integrally in said control bimetal leg disposed closer to said first end than to said second end of said leg, said lateral arm portion being bent at approximately a 90 angle relative to said control bimetal leg, at least a portion of said lateral arm being of reduced cross sectional area, and means to effect heating of said lateral arm portion upon closure of said contacts, whereby said first end of said control bimetal leg deflects in a first lateral direction away from said second contact and also deflects in a longitudinal direction to thus aid in opening said contacts.

2. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, resilient means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said control bimetal leg, a second contact carried by said base for co operation with said movable contact, adjustable means acting on said resilient means to adjust the relative position of said contacts, a lateral arm portion integrally in said control bimetal leg disposed closer to said first end than to said second end of said leg, said lateral arm portion being bent to form at least a 180 bend, and means connected to conduct current through said contacts and through said lateral arm portion of said control bimetal leg to effect heating thereof, whereby said first end of 6 said control bimetal leg deflects in a first lateral direction away from said second contact and also deflects in a longitudinal direction to thus aid in opening said contacts.

3. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, resilient means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said control bimetal leg, a second contact carried by said base for cooperation with said movable contact, adjustable means acting on said resilient means to adjust the relative position of said contacts, a lateral arm portion in said control bimetal leg disposed closer to said first end than to said second end of said leg, said lateral arm portion being bent to form approximately a bend, at least part of said lateral arm portion being of reduced cross sectional area, and means connected to conduct current through said contacts and through said lateral arm portion of said control bimetal leg to effect heating thereof, whereby said first end of said control bimetal leg deflects in a first lateral direction away from said second contact and also deflects in a longitudinal direction to thus aid in opening said contacts.

4. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, resilient means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said con trol bimetal leg, a second contact carried by said base for cooperation with said movable contact, adjustable means acting to adjust the relative position of said contacts, a portion of reduced cross sectional area in said control bimetal leg disposed closer to said first end than to said second end of said leg, said reduced cross sectional area portion being bent to form a small U-shape arm extending generally perpendicular to said control bimetal leg, and means connected to conduct current through said contacts and through said reduced portion of said control bimetal leg to effect heating thereof, whereby said first end of said control bimetal leg deflects in a first lateral direction away from said second contact and also deflects in a longitudinal direction to thus aid in opening said contacts despite any sticking thereof.

5. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, a resilient means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said control bimetal leg, 21 second contact carried by said base for cooperation with said movable contact, adjustable means acting on said resilient means to adjust the position of said movable contact relative to said second contact, a portion of reduced cross sectional area in said control bimetal leg disposed closer to said first end than to said second end of said leg, said reduced cross sectional area portion being bent to form a small U-shape arm extending generally perpendicular to said control bimetal leg, and means connected to said second end of said control bimetalleg toconduct current through said contacts and through said control bimetal leg to effect heating thereof, whereby said first end of said control bimetal leg defiects in a first lateral direction away from said second contact and also deflects in a longitudinal direction to thus aid in opening said contacts'despite any sticking thereof.

6. A thermostat, comprising, in combination, a base, a control bimetal leg having first and second ends, resilient means mounting said bimetal leg second end on said base, a movable contact carried on said first end of said control bimetal leg, a second contact carried by said base for cooperation with said movable contact, cam means acting on said resilient means to adjust the position of said movable contact relative to said second contact, a portion of reduced cross sectional area in said control bimetal leg disposed closer to said first end than to said second end of said leg, said reduced cross sectional area portion being bent to form a small U-shape arm extending generally perpendicular to said control bimetal leg and F Z toward said second contact, and means connected to said second end of said control bimetal leg to conduct current through said contacts and though said control bimetal leg to effect heating thereof, whereby said first end of said control bimetal leg deflects in a first lateral direction away from said second contact and also deflects in a longitudinal direction toward said second end of said control bimetal leg to thus aid in opening said contacts despite any sticking thereof.

7. A thermostat, comprising, in combination, a base, a resilient support blade having first and second ends with said second end fixedly mounted on said base, a control bimetal leg having first and second ends, means mounting said bimetal leg second end on said support blade first end, a fixed contact on said base, a movable contact carried on said first end of said control bimetal leg for cooperation with said fixed contact, cam means acting on said resilient support blade to adjust the position of said movable contact relative to said fixed contact, a portion of reduced cross-sectional area in said control bimetal leg disposed closer to said first end than to said second end of said leg, said reduced cross sectional area portion being bent to form a small U-shape arm extending generally perpendicular to said control bimetal leg and toward said fixed contact, and a flexible lead connected to said second end of said control bimetal leg to conduct current through said contacts and through said control bimetal leg to efiect heating thereof, whereby said first end of said control blmetal leg deflects in a first lateral direction away from said fixed contact and also deflects in a longitudinal direction toward said second end of said control bimetal leg to thus aid in opening said contacts despite any sticking thereof.

8. A thermostat, comprising, in combination, a base, a resilient support blade having first and second ends with said second end fixedly mounted on said base, a control bimetal leg having first and second ends, ambient com- V pensation means mounting said bimetal leg second end on said support blade first end, a fixed contact on said base, a movable contact carried on said first end of said control bimetal leg for cooperation with said fixed contact, can: means acting on said resilient support blade to adjust the position of said movable contact relative to said fixed contact, a portion of substantially uniform reduced cross sectional area in said control bimetal leg disposed at approximately one-third the distance from said'first to said second end of said leg, said reduced cross sectional area portion being bent to form a small U-shape arm extending gen erally perpendicular to said control bimetal leg and toward said fixed contact, and a flexible lead connected to said second end of said control bimetal leg to conduct current through said contacts and through said control bimetal leg to ettect heating thereof, whereby said first end of said control bimetal leg deflects in a first lateral direction away from said fixed contact and also deflects in a longitudinal direction toward said second end of said control bimetal leg to thus provide a wiping action between said contacts.

9. A thermostat, comprising, in combination, a base, a resilient support blade having first and second ends with said second end fixedly mounted on said base, a control bimetal leg and an ambient compensation bimetalleg each having first and second ends, means fixing said first end of said compensation bimetal leg on said first end of said support blade, an insulator joining said second ends of said bimetal legs to form a U-shape bimetal structure with said bimetal legs extending substantially parallel, an adjustably fixed contact on said base, a movable contact carried on said first end'of said control bimetal leg for cooperation with said fixed contact, cam means acting on said resilient support blade to adjust the position of said movable contact relative to said fixed contact, a portion or" reduced cross sectional area in said control bimetal leg disposed closer to said first end than to said second end of said leg, said reduced cross sectional area portion being of substantially constant width less than the width of the remainder of said control bimetal arm, said reduced cross sectional area portion being bent flatwise to form a small U-shape arm extending generally perpendicular to said control bimetal leg and toward said fixed contact, and a flexible lead connected to said second end of said control bimetal leg to conduct current through said contacts and through said control bimetal leg toeltect heating thereof,

whereby said first end of said control bimetal leg deflects in a first lateral direction away from said fixed contact and also deflects in a longitudinal direction toward said second end of said control bimetal leg to thus aid in opening said contacts despite any sticking thereof.

10. A thermostat for a controllable heating unit, comprising, in combination, a base, a resilient support blade having first and second ends, means mounting said second end fixedly on said base, a bimetallic leg with first and second ends, ambient temperature compensation means mounting said bimetallic leg second end on said support blade first end, a movable contact carried on said bimetallic leg first end, a fixed contact carried on said base for cooperation with said movable contact, first and second terminals on said base, means connecting said fixed contact to said first terminal, a flexible pigtail connecting said bimetallic leg second end to said second terminal, means connecting a'controllable heating unit through said first and second terminals to a voltage source for energizing said controllable heating unit, a cam acting on a medial portion of said support blade to change the position of said bimetallic leg relative to said base, said himetallic leg having a portion of reduced cross sectional area near said first end thereof, said reduced cross sectional area section being bent to form a small U-shaped arm extending generally perpendicular to said control bimetal leg and toward said fixed contact, whereby current to said controllable heating unit passes through said himetallic leg and through said reduced area portion to establish the greatest heat thereat to retard initial movement of said movable contact, and whereby said first end of said bimetal leg deflects in afirst lateral direction away from said fixed contact and also deflects in a longitudinal direction toward said second end of said bimetal leg to thus aid in opening said contacts despite any sticking thereof.

lteierences Cited by the Examiner UNlTED STATES PATENTS BERNARD A. GELHEANY, Primary Examiner. 

1. A THERMOSTAT, COMPRISING, IN COMBINATION, A BASE, A CONTROL BIMETAL LEG HAWVING FIRST AND SECOND ENDS, MEANS MOUNTING SAID BIMETAL LEG SECOND END ON SAID BASE, A MOVABLE CONTACT CARRIED ON SAID FIRST END OF SAID CONTROL BIMETAL LEG, A SECOND CONTACT CARRIED BY SAID BASE FOR COOPERATION WITH SAID MOVABLE CONTACT, A LATERAL ARM PORTION INTEGRALLY IN SAID CONTROL BIMETAL LEG DISPOSED CLOSER TO SAID FIRST END THAN TO SAID SECOND END OF SAID LEG, SAID LATERAL ARM PORTION BEING BENT AT APPROXIMATELY A 90* ANGLE RELATIVE TO SAID CONTROL BIMETAL LEG, AT LEAST A PORTION OF SAID LATERAL ARM BEING OF REDUCED CROSS SECTIONAL AREA, AND MEANS TO EFFECT HEATING OF SAID LATERAL ARM PORTION UPON CLOSURE OF SAID CONTACTS, WHEREBY SAID FIRST END OF SAID CONTROL BIMETAL LEG DEFLECTS IN A FIRST LATERAL DIRECTION AWAY FROM SAID SECOND CONTACT AND ALSO DEFLECTS IN A LONGITUDINAL DIRECTION TO THUS AID IN OPENING SAID CONTACTS. 